1. Field of the Invention
The invention relates to a magnetic resonance (MR) method for the reduction of motion artefacts in which a plurality of MR data sets concerning an object to be examined are acquired successively in time.
The invention also relates to an MR device for carrying out the method, including means for forming MR images from MR signals, a programmable control unit for controlling said means, and a reconstruction unit for reconstructing MR images by means of the projection reconstruction method.
2. Description of the Related Art
An MR method and MR device of this kind are known from U.S. Pat. No. 5,502,385. According to the method disclosed therein, MR sequences with continuously varied magnetic gradient fields act on the object to be examined. MR images are reconstructed from the MR signals thus generated, the oldest MR signals taken into account for the reconstruction of an MR image being replaced by the respective newly generated MR signals for the reconstruction of the next MR image. Dynamic processes taking place in the examination zone can then be reproduced with few artefacts by varying the direction of the magnetic gradient field applied during the generating of an MR signal from one sequence to another in such a manner that the range of magnetic gradient field directions required for the reconstruction is uniformly distributed between the respective newly generated MR signals.
Generally speaking, the acquisition of an MR data set of a moving object in order to form a high-resolution MR image requires a period of time which is not negligibly small in relation to the movement of the object. Because of the motion of the object to be examined in the course of the data acquisition, therefore, artefacts are liable to occur in the high-resolution MR image reconstructed by means of the known method. However, when a given resolution of the MR image is specified, the measuring time generally can be reduced to a very small extent only.